title: Regulation of ROS-independent ERK signaling rescues replicative cellular senescence in ex vivo expanded human c-kit-positive cardiac progenitor cells.
abstract: BACKGROUND
  Although the rescue of cellular senescence during ex vivo expansion of human-derived cardiac progenitor cells (hCPC) is critical for the application of autologous stem cell therapy in cardiovascular disease, the underlying molecular pathways during replicative senescence in hCPC have not been fully defined. Thus, we examined whether the regulation of mitogen-activated protein kinases activation could facilitate the recovery of human c-kit-positive hCPCs (hCPC(c-kit+)) and whether senescence is reactive oxygen species (ROS)-dependent or -independent.
  
  
  RESULTS
  To investigate the molecular pathways of replicative cellular senescence, we first evaluated cellular senescence in ex vivo-expanded hCPC(c-kit+) by using senescence-associated β-galactosidase (SA-β-gal) activity with enlarged cytoplasm and observed increased expression of cell senescence-related pivotal molecules, including TP53, cleavage Mdm2 (cMdm2), and Mdm2. Unexpectedly, we found that the extracellular signal-regulated kinase (ERK) was markedly activated in aged hCPC(c-kit+), with reduced proliferative activity. SA-β-gal activity and cytoplasm size in senescent hCPC(c-kit+) were significantly reduced, with reduced TP53 and cMdm2 expression after treatment with a specific ERK inhibitor (U0126). We examined whether the signaling in ERK inhibitory rescue of hCPC(c-kit+) senescence is ROS-dependent. Interestingly, the increased ROS level was not changed after treatment with a specific ERK inhibitor. Similarly, the increased expression levels of endogenous antioxidant enzymes, e.g., peroxiredoxin (Prdx)-1 and 2, in senescent hCPC(c-kit+) were not changed after treatment with a specific ERK inhibitor.
  
  
  CONCLUSIONS
  From the above results, we conclude that the specific inhibition of ERK during cellular senescence might rescue bioactivities of senescent hCPC(c-kit+) in a ROS-independent manner.
authors.affiliation: Laboratory of Cardiovascular Regeneration, Division of Cardiology, Seoul St. Mary's Hospital, The Catholic University of Korea School of Medicine, Seoul, South Korea.
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Choi
authors.forename: Seok Yun
authors.initials: SY
authors.lastname: Jung
authors.forename: So Young
authors.initials: SY
authors.lastname: Yoo
authors.forename: Sae Mi
authors.initials: SM
authors.lastname: Yoo
authors.forename: Da Yeon
authors.initials: DY
authors.lastname: Kim
authors.forename: Songhwa
authors.initials: S
authors.lastname: Kang
authors.forename: Sang Hong
authors.initials: SH
authors.lastname: Baek
authors.forename: Sang-Mo
authors.initials: SM
authors.lastname: Kwon
mesh_terms: D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013234:Stem Cells / Q000378:metabolism / Q000502:physiology*
chemical_list: D017382:Reactive Oxygen Species; D019009:Proto-Oncogene Proteins c-kit; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: Cardiac progenitor cell; ERK; Peroxiredoxin; Reactive oxygen species; Replicative senescence